The present invention pertains to heating and cooling systems, and more particularly to a multi-zone heating and cooling system incorporating a closed loop water circulation circuit and ventilation air control.
Multi-zone air heating and cooling systems having a plurality of reversible cycle units interconnected in a closed loop water circulation circuit are known. Further, such systems having ventilation air controls are also known.
In known systems comprising a plurality of reversible cycle units interconnected in a closed loop water circulation circuit, heat is extracted from the air passing through those units which are cooling and transferred to the water in the closed loop circuit wherein it accumulates for use by other units which are heating the air passing through them. The units which are heating air extract the accumulated heat from the water in the closed loop circuit to heat the air passing through them, thus, conserving energy.
In such systems, the water temperature must be maintained within a certain temperature range. If the water temperature falls below the lower limit of this range there will not be sufficient heat in the water for efficient heat transfer to the units which are heating the air passing through them. When the water temperature drops below the low temperature limit of the range supplemental heat must be added to it by means of a supplemental water heater. This, of course, requires the input of energy which is becoming increasingly costly.
Other known systems of this type also include an out-of-doors air ventilation-cooling system. In addition to merely adding some amount of out-of-doors air sufficient for ventilation purposes, these systems also provide an adequate amount of out-of-doors air, over and above that amount which may be required for merely ventilation purposes, to provide a natural cooling of the air within a building zone served by, at least one of, the reversible cycle units of the system. When the out-of-doors air temperature is below the zone air temperature of a zone requiring cooling, the compressor of the reversible cycle unit serving that zone is deactivated and the cooler out-of-doors air is conveyed to the served zone, thus, cooling the served zone air and conserving the energy which would otherwise be consumed by the compressor. As long as the out-of-doors air temperature is below the air temperature in a zone requiring cooling, out-of-doors air is used for cooling and the compressor of the unit serving that zone remains deactivated, regardless of the temperature of the water in the closed loop circuit. While out-of-doors air is being used to cool the served zone air, no heat is being transferred by the unit serving that zone to the water in the closed water loop circuit. Thus, gradually the temperature of the water in the closed loop drops as other units of the system in a heating mode of operation extract heat from the water in the closed loop circuit. In time, the temperature of the water drops below the low temperature limit of the required water temperature range and the supplemental heater is activated to heat the water back into the required range.
This presents a problem to which the prior art does not address itself. At this point, there exists two conflicting operating conditions. One condition (cooling of zones using out-of-doors air) saving energy, and the other condition (using a supplementary heater to heat the water in the closed loop) expending energy. Unfortunately, these two conditions do not balance each other. It has been determined in practice that it requires more energy to add the necessary heat to the water by means of, for example, an electric heater than is used by the compressor in transferring the same amount of necessary heat from the air in the overheated space or space requiring cooling to the water.